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<a name="Functions-In-Python"></a>
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<p>
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<hr>
<a name="Writing-new-convenience-functions"></a>
<h4 class="subsubsection">23.2.2.21 Writing new convenience functions</h4>

<a name="index-writing-convenience-functions"></a>
<a name="index-convenience-functions-in-python"></a>
<a name="index-python-convenience-functions"></a>
<a name="index-gdb_002eFunction"></a>
<a name="index-Function"></a>
<p>You can implement new convenience functions (see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>)
in Python.  A convenience function is an instance of a subclass of the
class <code>gdb.Function</code>.
</p>
<dl>
<dt><a name="index-Function_002e_005f_005finit_005f_005f"></a>Function: <strong>Function.__init__</strong> <em>(name)</em></dt>
<dd><p>The initializer for <code>Function</code> registers the new function with
<small>GDB</small>.  The argument <var>name</var> is the name of the function,
a string.  The function will be visible to the user as a convenience
variable of type <code>internal function</code>, whose name is the same as
the given <var>name</var>.
</p>
<p>The documentation for the new function is taken from the documentation
string for the new class.
</p></dd></dl>

<dl>
<dt><a name="index-Function_002einvoke"></a>Function: <strong>Function.invoke</strong> <em>(<var>*args</var>)</em></dt>
<dd><p>When a convenience function is evaluated, its arguments are converted
to instances of <code>gdb.Value</code>, and then the function&rsquo;s
<code>invoke</code> method is called.  Note that <small>GDB</small> does not
predetermine the arity of convenience functions.  Instead, all
available arguments are passed to <code>invoke</code>, following the
standard Python calling convention.  In particular, a convenience
function can have default values for parameters without ill effect.
</p>
<p>The return value of this method is used as its value in the enclosing
expression.  If an ordinary Python value is returned, it is converted
to a <code>gdb.Value</code> following the usual rules.
</p></dd></dl>

<p>The following code snippet shows how a trivial convenience function can
be implemented in Python:
</p>
<div class="smallexample">
<pre class="smallexample">class Greet (gdb.Function):
  &quot;&quot;&quot;Return string to greet someone.
Takes a name as argument.&quot;&quot;&quot;

  def __init__ (self):
    super (Greet, self).__init__ (&quot;greet&quot;)

  def invoke (self, name):
    return &quot;Hello, %s!&quot; % name.string ()

Greet ()
</pre></div>

<p>The last line instantiates the class, and is necessary to trigger the
registration of the function with <small>GDB</small>.  Depending on how the
Python code is read into <small>GDB</small>, you may need to import the
<code>gdb</code> module explicitly.
</p>
<p>Now you can use the function in an expression:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) print $greet(&quot;Bob&quot;)
$1 = &quot;Hello, Bob!&quot;
</pre></div>

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